Earth worm population dynamics in the oil palm ecosystem on coastal and inland soils of United Plantations Berhad

Earthworms are known as nature's cultivators of soil. Feeding on organic matter, their populations are known to be a common bioindicator of soil health. The oil palm being a perennial crop with an economic lifespan of about 25 years, it harbours various flora and fauna including earthworms in its ecosystem. An earthworm population study was initiated on the coastal, inland and organic soils of United Plantations Berhad planted with oil palm. Population census was carried out on 4 main sections of the oil palm field which includes the harvesters' path, non-harvesting avenue, under the frond heaps and in the palm circle. Earthworms from the soil was extracted using a vermifuge applied on an area of 0.25 m² using a metal ring. Highest earthworm population was noted on the Bungor series at 513600 worms per hectare while the heavy marine alluvial clay soils recorded lower populations with the Briah series giving the lowest count at 61300 worms per hectare. Earthworm populations were found to be absent on organic soils. Distribution within the field varied between soil types but generally higher populations were noted under the frond heaps and the non-harvesting avenues which have the highest organic matter and which are least disturbed areas. The dominant earthworm species found on all the soil types were the Pontoscolex corenthurus, an endogeic earthworm native to Malaysia. Nutrient analysis of the earthworm castings from the various soil types was also carried out and the results were compared to the nutrient content of the in situ soil. It was noted that the castings, in general, had higher nitrogen content compared to the soil in which they were present. This preliminary study shows that there is a satisfactory population of earthworms in the oil palm rhizosphere on the mineral soils. Further studies are on going on augmentation in areas where the population is low as well as long term evaluation of the benefits of earthworms in oil palm production.